Study of the Lipid Profile of ATCC and Clinical Strains of Staphylococcus aureus in Relation to Their Antibiotic Resistance

Antifungal activity of aminopyrrolnitrin against Trichophyton verrucosum in a guinea pig model of dermatophytosis

BACKGROUND

Dermatophytosis is a common and major public health concern worldwide. Despite the increasing availability of antifungal drugs, relapses and untreated cases of dermatophyte infections are reported. Therefore, novel antifungal agents are required. Aminopyrrolnitrin (APRN) shows promise for dermatophytosis treatment because of its antifungal activity.

OBJECTIVES

This study aimed to assess the antifungal properties of APRN against Trichophyton verrucosum (T. verrucosum), in both laboratory settings and a guinea pig model.

METHODS

The minimum inhibitory concentrations (MICs) of APRN and enilconazole against T. verrucosum were determined according to the CLSI M38 method. The skins of 16 male guinea pigs were infected with 1.0 × 108 conidia of T. verrucosum and the animals were grouped into sets of four: negative control group (NC) received normal saline; positive control group (PC) received 2 μg/mL of enilconazole; and APRN4 and APRN8 received 4 and 8 μg/mL of APRN, respectively. Clinical, mycological and histological efficacies were measured after 10 days.

RESULTS

The MIC90 of APRN and enilconazole against T. verrucosum was 4 and 2 μg/mL, respectively. The clinical scores of PC, APRN4, and APRN8 were significantly lower than those of NC. Clinical and mycological efficacies were higher for APRN8, APRN4 and PC. No fungi were observed in the skin tissues of APRN4 and APRN8, while fungi were observed in 50% of the PC.

CONCLUSION

APRN showed antifungal activity against T. verrucosum in vitro and in vivo and is a potential candidate for the treatment of dermatophytosis.

Bacterial extracellular vesicles: towards realistic models for bacterial membranes in molecular interaction studies by surface plasmon resonance

One way to mitigate the ongoing antimicrobial resistance crisis is to discover and develop new classes of antibiotics. As all antibiotics at some point need to either cross or just interact with the bacterial membrane, there is a need for representative models of bacterial membranes and efficient methods to characterize the interactions with novel molecules -both to generate new knowledge and to screen compound libraries. Since the bacterial cell envelope is a complex assembly of lipids, lipopolysaccharides, membrane proteins and other components, constructing relevant synthetic liposome-based models of the membrane is both difficult and expensive. We here propose to let the bacteria do the hard work for us. Bacterial extracellular vesicles (bEVs) are naturally secreted by Gram-negative and Gram-positive bacteria, playing a role in communication between bacteria, as virulence factors, molecular transport or being a part of the antimicrobial resistance mechanism. bEVs consist of the bacterial outer membrane and thus inherit many components and properties of the native outer cell envelope. In this work, we have isolated and characterized bEVs from one Escherichia coli mutant and three clinical strains of the ESKAPE pathogens Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa. The bEVs were shown to be representative models for the bacterial membrane in terms of lipid composition with speciesstrain specific variations. The bEVs were further used to probe the interactions between bEV and antimicrobial peptides (AMPs) as model compounds by Surface Plasmon Resonance (SPR) and provide proof-of-principle that bEVs can be used as an easily accessible and highly realistic model for the bacterial surface in interaction studies. This further enables direct monitoring of the effect induced by antibiotics, or the response to host-pathogen interactions.

Antimicrobial Susceptibility of Staphylococcus aureus Strains and Effect of Phloretin on Biofilm Formation

Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) are known to be responsible of various infections, including biofilm-associated diseases. The aim of this study was to analyze 19 strains of S. aureus from orthopedic sites in terms of phenotypic antimicrobial susceptibility against 13 selected antibiotics, slime/biofilm formation, molecular analysis of specific antibiotic resistance genes (mecA, cfr, rpoB), and biofilm-associated genes (icaADBC operon). Furthermore, the effect of phloretin on the production of biofilm was evaluated on 8 chosen isolates. The susceptibility test confirmed almost all strains were resistant to cefoxitin and oxacillin. Most strains possess the mecA, whereas none of the strains had the cfr gene. Four strains (1, 7, 10, and 24) presented single-nucleotide polymorphisms (SNPs) in rpoB, which confer rifampicin resistance. IcaD was detected in all tested strains, whereas icaR was only found in two strains (24 and 30). Phloretin had a dose-dependent effect on biofilm production. Specifically, 0.5 × MIC determined biofilm inhibition in 5 out of 8 strains (8, 24, 25, 27, 30), whereas an increase in biofilm production was detected with phloretin at the 0.125 × MIC across all tested strains. These data are useful to potentially develop novel compounds against antibiotic-resistant S. aureus.

Nano-Hybrid Ag@LCCs Systems with Potential Wound-Healing Properties

The synthesis of contaminant-free silver@linear carbon chains (Ag@LCCs) nanohybrid systems, at different Ag/LCCs ratios, by pulsed laser ablation was studied. The ablation products were first characterized by several diagnostic techniques: conventional UV-Vis optical absorption and micro-Raman spectroscopies, as well as scanning electron microscopy, operating in transmission mode. The experimental evidence was confirmed by the theoretical simulations' data. Furthermore, to gain a deeper insight into the factors influencing metal@LCCs biological responses in relation to their physical properties, in this work, we investigated the bioproperties of the Ag@LCCs nanosystems towards a wound-healing activity. We found that Ag@LCC nanohybrids maintain good antibacterial properties and possess a better capability, in comparison with Ag NPs, of interacting with mammalian cells, allowing us to hypothesize that mainly the Ag@LCCs 3:1 might be suitable for topical application in wound healing, independent of (or in addition to) the antibacterial effect.

“Omic” Approaches to Bacteria and Antibiotic Resistance Identification

The quick and accurate identification of microorganisms and the study of resistance to antibiotics is crucial in the economic and industrial fields along with medicine. One of the fastest-growing identification methods is the spectrometric approach consisting in the matrix-assisted laser ionization/desorption using a time-of-flight analyzer (MALDI-TOF MS), which has many advantages over conventional methods for the determination of microorganisms presented. Thanks to the use of a multiomic approach in the MALDI-TOF MS analysis, it is possible to obtain a broad spectrum of data allowing the identification of microorganisms, understanding their interactions and the analysis of antibiotic resistance mechanisms. In addition, the literature data indicate the possibility of a significant reduction in the time of the sample preparation and analysis time, which will enable a faster initiation of the treatment of patients. However, it is still necessary to improve the process of identifying and supplementing the existing databases along with creating new ones. This review summarizes the use of “-omics” approaches in the MALDI TOF MS analysis, including in bacterial identification and antibiotic resistance mechanisms analysis.

Effect of Vancomycin on Cellular Fatty Acid Profiles of Vancomycin-Susceptible and Nonsusceptible Staphylococcus aureus

Vancomycin is widely used for treatment of infection caused by methicillin-resistant Staphylococcus aureus (MRSA) leading to an increasing appearance of low-level vancomycin-resistant isolates called heterogeneous vancomycin-intermediate S. aureus (hVISA). The mechanism of vancomycin tolerance in hVISA is still unclear. This study aimed to investigate the fatty acid compositions of S. aureus isolates under the stress environment with vancomycin. The different responses of hVISA and vancomycin-susceptible S. aureus (VSSA) may lead to more understanding the mechanism. The bacterial lipid profiles were tested three times from three extractions of each isolate cultured on tryptic soy agar (TSA) and TSA with vancomycin. Of the 30 MRSA isolates studied, 13, 12, and 5 isolates were VSSA, hVISA, and VISA, respectively. The analysis of bacterial lipid profiles showed that under vancomycin stress, there was a reduction of straight chain fatty acids (SCFAs) in VSSA isolates but an increase in branched chain fatty acids (BCFAs). In contrast, the hVISA group exhibited an increase only in the BCFAs but not in SCFAs. Of interest, vancomycin had no effect on either BCFAs or SCFAs of the VISA cells. This study provided information of bacterial adaptation during stress with vancomycin that may be helpful to overcome the resistant bacteria.

Phytochemical Characterization of Olea europea Leaf Extracts and Assessment of Their Anti-Microbial and Anti-HSV-1 Activity

Owing to the richness of bioactive compounds, Olea europea leaf extracts exhibit a range of health effects. The present research evaluated the antibacterial and antiviral effect of leaf extracts obtained from Olea europea L. var. sativa (OESA) and Olea europea var. sylvestris (OESY) from Tunisia. LC-DAD-ESI-MS analysis allowed the identification of different compounds that contributed to the observed biological properties. Both OESA and OESY were active against Gram-positive bacteria (MIC values between 7.81 and 15.61 μg/mL and between 15.61 and 31.25 μg/mL against Staphylococcus aureus ATCC 6538 for OESY and OESA, respectively). The antiviral activity against the herpes simplex type 1 (HSV-1) was assessed on Vero cells. The results of cell viability indicated that Olea europea leaf extracts were not toxic to cultured Vero cells. The half maximal cytotoxic concentration (CC₅₀) values for OESA and OESY were 0.2 mg/mL and 0.82 mg/mL, respectively. Furthermore, both a plaque reduction assay and viral entry assay were used to demonstrate the antiviral activity. In conclusion, Olea europea leaf extracts demonstrated a bacteriostatic effect, as well as remarkable antiviral activity, which could provide an alternative treatment against resistant strains.

Colistin Treatment Affects Lipid Composition of Acinetobacter baumannii

Multidrug-resistant Acinetobacter baumannii (A. baumannii) causes severe and often fatal healthcare-associated infections due partly to antibiotic resistance. There are no studies on A. baumannii lipidomics of susceptible and resistant strains grown at lethal and sublethal concentrations. Therefore, we analyzed the impact of colistin resistance on glycerolipids’ content by using untargeted lipidomics on clinical isolate. Nine lipid sub-classes were annotated, including phosphatidylcholine, rarely detected in the bacterial membrane among 130 different lipid species. The other lipid sub-classes detected are phosphatidylethanolamine (PE), phosphatidylglycerol (PG), lysophosphatidylethanolamine, hemibismonoacylglycerophosphate, cardiolipin, monolysocardiolipin, diacylglycerol, and triacylglycerol. Under lethal and sublethal concentrations of colistin, significant reduction of PE was observed on the resistant and susceptible strain, respectively. Palmitic acid percentage was higher at colistin at low concentration but only for the susceptible strain. When looking at individual lipid species, the most abundant PE and PG species (PE 34:1 and PG 34:1) are significantly upregulated when the susceptible and the resistant strains are cultivated with colistin. This is, to date, the most exhaustive lipidomics data compilation of A. baumannii cultivated in the presence of colistin. This work is highlighting the plasma membrane plasticity used by this gram-negative bacterium to survive colistin treatment.

Increased Antibiotic Resistance of Methicillin-Resistant Staphylococcus aureus USA300 Δpsm Mutants and a Complementation Study of Δpsm Mutants Using Synthetic Phenol-Soluble Modulins

Phenol-soluble modulins (PSMs) are responsible for regulating biofilm formation, persister cell formation, pmtR expression, host cell lysis, and anti-bacterial effects. To determine the effect of psm deletion on methicillin-resistant Staphylococcus aureus, we investigated psm deletion mutants including Δpsmα, Δpsmβ, and Δpsmαβ;. These mutants exhibited increased β-lactam antibiotic resistance to ampicillin and oxacillin that was shown to be caused by increased Nacetylmannosamine kinase (nanK) mRNA expression, which regulates persister cell formation, leading to changes in the pattern of phospholipid fatty acids resulting in increased anteiso-C_15:0, and increased membrane hydrophobicity with the deletion of PSMs. When synthetic PSMs were applied to Δpsmα and Δpsmβ mutants, treatment of Δpsmα with PSMα1-4 and Δpsmβ with PSMβ1-2 restored the sensitivity to oxacillin and slightly reduced the biofilm formation. Addition of a single fragment showed that α1, α2, α3, and β2 had an inhibiting effect on biofilms in Δpsmα; however, β1 showed an enhancing effect on biofilms in Δpsmβ. This study demonstrates a possible reason for the increased antibiotic resistance in psm mutants and the effect of PSMs on biofilm formation.

Combination Therapy Using Low-Concentration Oxacillin with Palmitic Acid and Span85 to Control Clinical Methicillin-Resistant Staphylococcus aureus

The overuse of antibiotics has led to the emergence of multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA). MRSA is difficult to kill with a single antibiotic because it has evolved to be resistant to various antibiotics by increasing the PBP2a (mecA) expression level, building up biofilm, introducing SCCmec for multidrug resistance, and changing its membrane properties. Therefore, to overcome antibiotic resistance and decrease possible genetic mutations that can lead to the acquisition of higher antibiotic resistance, drug combination therapy was applied based on previous results indicating that MRSA shows increased susceptibility to free fatty acids and surfactants. The optimal ratio of three components and the synergistic effects of possible combinations were investigated. The combinations were directly applied to clinically isolated strains, and the combination containing 15 μg/mL of oxacillin was able to control SCCmec type III and IV isolates having an oxacillin minimum inhibitory concentration (MIC) up to 1024 μg/mL; moreover, the combination with a slightly increased oxacillin concentration was able to kill SCCmec type II. Phospholipid analysis revealed that clinical strains with higher resistance contained a high portion of 12-methyltetradecanoic acid (anteiso-C15:0) and 14-methylhexadecanoic acid (anteiso-C17:0), although individual strains showed different patterns. In summary, we showed that combinatorial therapy with a low concentration of oxacillin controlled different laboratory and highly diversified clinical MRSA strains.

Antibacterial Activity of Hexadecynoic Acid Isomers toward Clinical Isolates of Multidrug-Resistant Staphylococcus aureus

In the present study, the structural characteristics that impart antibacterial activity to C₁₆ alkynoic fatty acids (aFA) were further investigated. The syntheses of hexadecynoic acids (HDA) containing triple bonds at C-3, C-6, C-8, C-9, C-10, and C-12 were carried out in four steps and with an overall yield of 34-78%. In addition, HDA analogs containing a sulfur atom at either C-4 or C-5 were also prepared in 69-77% overall yields, respectively. Results from this study revealed that the triple bond at C-2 is pivotal for the antibacterial activity displayed by 2-HDA, while the farther the position of the triple bond from the carbonyl group, the lower its bactericidal activity against gram-positive bacteria, including clinical isolates of methicillin-resistant Staphylococcus aureus (CIMRSA) strains. The potential of 2-HDA as an antibacterial agent was also assessed in five CIMRSA strains that were resistant to Ciprofloxacin (Cipro) demonstrating that 2-HDA was the most effective treatment in inhibiting their growth when compared with either Cipro alone or equimolar combinations of Cipro and 2-HDA. Moreover, it was proved that the inhibition of S. aureus DNA gyrase can be linked to the antibacterial activity displayed by 2-HDA. Finally, it was determined that the ability of HDA analogs to form micelles can be linked to their decreased activity against gram-positive bacteria, since critical micellar concentrations (CMC) between 50 and 300 μg/mL were obtained.

The Antimicrobial and Antiviral Activity of Polyphenols from Almond (Prunus dulcis L.) Skin

Due to their antimicrobial and antiviral activity potential in vitro, polyphenols are gaining a lot of attention from the pharmaceutical and healthcare industries. A novel antiviral and antimicrobial approach could be based on the use of polyphenols obtained from natural sources. Here, we tested the antibacterial and antiviral effect of a mix of polyphenols present in natural almond skin (NS MIX). The antimicrobial potential was evaluated against the standard American Type Culture Collection (ATCC) and clinical strains of Staphylococcus aureus, including methicillin-resistant (MRSA) strains, by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Herpes simplex virus type I was used for the antiviral assessment of NS MIX by plaque assay. Furthermore, we evaluated the expression of viral cascade antigens. NS MIX exhibited antimicrobial (MIC values of 0.31–1.25 mg/ml) and antiviral activity (decrease in the viral titer ** p < 0.01, and viral DNA accumulation * p < 0.05) against Staphylococcus aureus and HSV-1, respectively. Amongst the isolated compounds, the aglycones epicatechin and catechin showed the greatest activity against S. aureus ATCC 6538P (MIC values of 0.078–0.15 and 0.15 mg/ml, respectively), but were not active against all the other strains. These results could be used to develop novel products for topical use.

Feijoa Fruit Peel: Micro-morphological Features, Evaluation of Phytochemical Profile, and Biological Properties of Its Essential Oil

Acca sellowiana (O. Berg) Burret (Feijoa) is an evergreen shrub, belonging to the Mirtaceae family. The aim of this study was to investigate the micromorphological features of the feijoa fruit peel and to evaluate the phytochemical profile, as well as the antioxidant, cytoprotective, and antimicrobial properties of its essential oil (EO), by several in vitro cell-free and cell-based assays. The micromorphological analysis showed several schizogenic secretory cavities, immediately below the epidermal layer. Forty compounds were identified and quantified by GC-FID and GC-MS analyses. Sesquiterpenes were the most abundant ones (76.89%), followed by monoterpene hydrocarbons (3.26%), and oxygenated monoterpenes (0.34%). The main compounds were γ-Selinene (17.39%), α-Cariophyllene (16.74%), β-Cariophyllene (10.37%), and Germacene D (5.32%). The EO showed a strong and dose-dependent antioxidant, and free-radical scavenging activity. Furthermore, it showed cytoprotective activity on the lymphocytes, that have been pre-treated with 100 μM tert-butyl-hydroperoxide (t-BOOH), as well as a decrease in intracellular reactive oxygen species (ROS), induced by t-BOOH on erythrocytes. A preliminary antimicrobial screening against GRAM+ and GRAM− bacteria, as well as on fungi highlighted that EO showed the best activity against S. aureus and C. albicans (MIC 2.7 mg/mL). In light of these results, feijoa fruit EO could find various applications, especially in the food, nutraceutical, and pharmaceutical fields.